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THIS group includes the Seals, Sea-Lions, and Walruses,1 all
aquatic and, for the larger part, marine creatures. Being aquatic
they have to some .extent acquired a fish-like form, though not
so completely as have the "Whales and even the Sirenia. This
is most complete so far as the group is concerned in the Seals,
where the hind-limbs have become soldered to the tail and are
inefficient as walking legs, where the external ears have vanished,
and where the general shape of the body is tapering and thus
fish-like. The Walruses and Sea-Lions are less modified in this
direction; in the latter (not in the former) the external ear,
though small, is persistent, and the hind-limbs are capable of
being used as organs of progression upon dry land. The general
characters applicable to the Carnivora, given upon a previous
page, apply to the Pinnipedia.
The characters confined to the Pinnipedia as a whole are
mainly these:—The greater part of the limbs are enclosed
within the skin, the hands and feet are fully webbed, and
there is a tendency for the nails to disappear, and for the
phalanges to increase in number—characters which are clearly
not diagnostic of the order but correlated with an aquatic
life, since they reappear, and are indeed exaggerated, in the
Cetacea. The teeth are peculiar in that the milk dentition is
feeble and is early shed. This, as it were, undue emphasis upon
one of the two sets of teeth is another likeness to the Whales,
1 For tlie genera of Pinnipedia see Mivart, Proc, Zool. Soc. 1885, p. 484,